Background The prevalence of patent foramen ovale (PFO) in the general population is about 25%. Most patients with a PFO as an isolated finding are asymptomatic and receive no special treatment; yet it is likely associated with cryptogenic stroke. Objective To assess the prevalence of PFO in patients with cryptogenic stroke or transient ischemic attacks (TIAs). Material and Methods We conducted a retrospective analysis of the transesophageal echocardiograms of patients with cryptogenic stroke or TIAs who were referred to our center to evaluate for an embolic source. The diagnosis of PFO was defined as the presence of a single microbubble in the first three beats after right atrium opacification. Atrial septum aneurysm (ASA) was diagnosed when the interatrial septum was abnormally redundant with an excursion of more than 10 mm into the right or left atrium. Results A total of 43 patients were evaluated; mean age was 59.6± 16.9 years, and 41.9% were women. Patent foramen ovale was detected in 13 patients (30.2%; 95% CI, 15% to 44%), 7 of whom (16.3% of the total population) had large defects. ASA was present in 6 patients (14%) associated with PFO; 4 patients (66%) had large PFOs. Conclusions The prevalence of PFO in patients with cryptogenic stroke or TIAs is 30%, and in 33% of cases it is associated with atrial septum aneurysm.